A grating is a component for measuring based on distance between lines on the grating. The grating may be classified into geometrical grating (amplitude grating) and diffraction grating (phase grating) according to different principles of forming moire fringes. The geometrical grating is adopted in micro-scale and submicron-scale grating measurement, in which a grating pitch of 100 to 20 μm is much greater than light wavelengths of light sources and diffraction phenomenon can be negligible. When two gratings move with respect to each other, low frequency beat phenomenon is generated and thus moire fringes are formed. This measurement principle is referred to as an image principle. The diffraction grating is adopted in nano-scale grating measurement, in which a grating pitch is 8 or 4 μm, a width of line is very close to wavelength of light, and diffraction and interference phenomena are generated and thus moire fringes are formed. This measurement principle is referred to as an interference principle.
The grating includes a light transmission portion (hereinafter referred to as “slit width”) and a light shielding portion (hereinafter referred to as “grid”), and thereby light incident on the grating is divided into several light beams. This allows the diffraction grating to be irradiated by the light beams having spatial coherence. The diffraction grating diffracts light from a source grating, and forms an interference pattern according to the Talbot effect. A light detector detects the light from the diffraction grating. In a grating-based X-ray phase contrast imaging system, an X-ray absorbing grating shall be arranged behind an X-ray source. A portion (grid) of the X-ray absorbing grating in which a heavy metal is filled absorbs X rays, and X rays transmit through the other portion (grating slit) of the grating, such that the absorbing grating and the common grating X-ray source conjointly form an X-ray source having one-dimensional spatial coherence.
As known, as the radiation imaging technology continuously develops, a higher imaging precision is required and thereby components in imaging devices shall have more precise dimensions. For example, there is a high requirement on gratings in radiation imaging devices. Existing methods for manufacturing gratings mainly include mechanical ruling, laser holographic lithography and electron beam lithography. The mechanical ruling has very strict requirements and following disadvantages: long processing time, low precision, high production difficulty, and hard to rule sub-micron lines. The electron beam lithography is able to form nano-scale high resolution pattern, but has a very low efficiency and cannot form patterns with high aspect ratios. The laser holographic lithography is able to form gratings in deep sub-micron levels, but has a high control precision, high cost and low productivity.